With social and economic development and the advance of globalization and informatization, cities are playing an increasingly important role in regional development, the social and economic linkages between cities in a region are closer and more complex, and internal connectivity in a metropolitan area has more significant influence on the defining of the range of each circle in the metropolitan area.
So far, in the field of urban planning, a metropolitan area is usually defined by using an economic geography model, such as an economic distance method, an economic gravity method, and an economic field strength method, the economic impact of a central city to the other cities around is simply calculated through economic data of each city and distance data between the cities, and the range of a metropolitan area is defined according to the degree of the impacts. Such method has the problems of limited perspectives and limited elements, and does not concern social factors, other than direct economic impact, that influence the inter-city association degree. Besides, an existing defining method usually judges interval values of economic impact of a central city to the other cities by subjective views and experience, and member cities in each circle of a metropolitan area are determined accordingly. In view of the above, the existing conventional method for defining circles of a metropolitan area has many problems, and is inapplicable to large-scale regional city analysis.